Water to drink a day
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This is total fluids. About a fifth usually comes from food.
A person who weighs 70 kg and exercises for 30 minutes needs about 70 × 33 = 2,310 ml, plus 350 ml: 2.7 litres a day, or about 11 glasses.
A common guide is about 30 to 35 ml for each kilogram you weigh (about half an ounce per pound), plus more when you exercise or it's hot. That's total fluids: water, tea, coffee, milk and the water in food all count.
Yes. Coffee and tea are mostly water. The mild effect of caffeine on how much you pee doesn't cancel out what you drink, for people used to it.
Pale yellow urine and rarely feeling thirsty are good signs. Dark yellow urine, headaches and tiredness can mean you need more.
It's rare, but drinking very large amounts quickly (several litres in an hour or two) can be dangerous. Spread your water through the day. People with heart or kidney conditions should follow their doctor's advice.